Prior Art
Paint rollers are widely used by professionals and amateurs for applying paint to walls, ceilings, and other surfaces. Typically the roller is used with an applicator having a handle terminating in a rotatable member to which the roller is secured. The roller itself generally comprises a paint absorbing and spreading cover affixed to a generally cylindrical core. The covers may be made from materials such as wool or polyester, and other cover materials that are well known in the art.
Years ago paint rollers were manufactured using a paper or chipboard core. Some manufacturers still make such paper core paint rollers. The manufacture of such cores is well known. Such cores, however, and the paint rollers made out of them, would often fall apart during use or during cleaning, especially during cleaning with paint solvents (such as, for example, turpentine or mineral spirits, such paint solvents are well known in the art). It has always been desirable, and still remains desirable, to make the paint roller resistant to paint solvents.
An advance in making paint rollers came when the paper cores were replaced with phenolic cores, that is, cores made from paper impregnated with phenolic. Such paint rollers withstood exposure to paint solvents much better than their paper or chipboard counterparts. The process of manufacturing phenolic cores is also well known. For example, according to one known technique, a reusable disposable roller is made by first feeding three phenolic impregnated paper strips at an angle to a mandrel for overlapping, helical winding to form an endless core. Typically, the phenolic strips are supplied in rolls that can be mounted on spindles for continuous feeding, and a continuous thermosetting glue is applied to the outer surfaces of the strips as they feed off the rollers such that the strips adhere together as they are helically wound to form the core. As the endless core is belt driven down the line, the core is heated in a multi-stage infrared heater, after which a hot melt glue is applied to the core's outer surface and a continuous strip of the cover material, such as polyester, is helically wound on to the core where it is secured by the hot melt. All that remains is to cut the resulting endless roller down to usable sizes, which is usually accomplished in two steps, first using a fly away cutter to cut, e.g., 65 inch stock, and then using another cutter to cut the stock into usable lengths of, e.g., seven or nine inches.
The obvious drawback of reusable cores formed in this manner is that they require a long assembly line, due to the need of a heater, and because the phenolic must be heated to a predetermined temperature, there is an obvious trade off between the number of heater stages and the speed of the line. Additionally, while the resulting rollers are termed reusable because they do not separate when placed in paint solvents, any prolonged exposure to such solvents, does result in breakdown of the paint roller and/or separation of the layers. Moreover, the manufacturing process for making phenolic core rollers is environmentally unfriendly.
Another reusable roller is disclosed in U.S. Pat. No. 4,692,975 issued to Garcia, wherein the roller is formed using a preformed core made of thermoplastic (e.g. polypropylene) tubular stock. In particular, the process disclosed mounting a preformed core on a rotating spindle, providing a carriage movable in a direction parallel to the spindle, and providing on the carriage a direct heat source and, at an angle to the spindle a continuous strip of fabric. The disclosed process consisted of igniting the direct heat source to begin heating the outer surface of the tubular stock and moving the carriage parallel to the spindle in timed relation to the spindle's rotation so that the fabric strip is wound on the heated portion of the plastic core in a tight helix. The heated portion of the plastic core was thereby heat-softened just in advance of the point where the fabric strip is applied, such that the fabric is bonded to the core as it is wound thereon. In effect, a portion of the it polypropylene core surface is used as the bonding adhesive. One advantage of the roller disclosed in the Garcia patent is that the bond formed between cover and core is a strong one not easily subject to separation from exposure to paint solvents. Another advantage is that the manufacturing process does not require the application of a separate adhesive to bond the cover to the core. There are, however, drawbacks. For one, while prior art techniques use rolls of, e.g., chipboard or paper, the Garcia process requires preformed thermoplastic tubular cores which are considerably bulkier than rolls, more expensive to transport, and more difficult to handle. Another drawback is the anticipated speed limit of the Garcia process dictated by the necessity that the heater, which advances along the core just in front of the fabric strip, move slow enough to insure softening of the polypropylene core, in the absence of which the fabric cover will not bond. In addition, the application of direct heat to the preformed polypropylene core presents manufacturing hazards from the heat source and from the fumes and/or chemicals released during the heating process.
U.S. Pat. No. 5,195,242 issued to the present inventor resolved many of the foregoing problems by (i) forming the thermoplastic core on the fly instead of using preformed cores, and (ii) using preheated thermoplastic as a glue, both to form the core by applying it between the strips forming the core, and to affix the cover to the core by applying it to the outside of the core before wrapping the cover thereabout. The patent describes a process involving the wrapping of three strips of thermoplastic material (preferably polypropylene) around a mandrel in overlapping relation to form a core, the strips making the core are bonded together by applying a liquefied thermoplastic material (again, preferably polypropylene) thereto prior to wrapping them about the mandrel. After the core is thus formed a liquefied thermoplastic (again, preferably polypropylene) is applied to the outer surface of the core, and a cover wrapped thereupon. All that remains, as is well known, is to cut the resulting endless roller down to usable sizes, which, as described above may be accomplished in two steps, first using a fly away cutter to make longer lengths, and then using another cutter to cut the stock into usable lengths. While this process was capable of making high quality rollers that were substantially unaffected by paint solvents, the process involved the use of multiple strips of thermoplastic material and numerous points of application for liquefied thermoplastic. As a result, the process was difficult to set up, and required many continuous adjustments in its operation.
U.S. Pat. No. 5,468,207 issued to Bower discloses a continuous process like that disclosed in the '242 patent, except that Bower discloses using direct heat to bond the surface of the thermoplastic plastic strips instead of applying liquefied thermoplastic to the strips to bond them together. Additionally, Bower discloses using direct heat to the surface of the core to bond the cover rather than applying liquefied thermoplastic prior to applying the cover.
U.S. Pat. No. 5,572,790, also issued to the present inventor, among other things, resolved some of the complexity problems of the foregoing process. Under this process, which has become the de facto standard for roller manufacturing today, instead of forming a core by winding a plurality of strips in overlapping relation about a mandrel, and then affixing a cover thereto, it was disclosed to wind only a single strip about the mandrel, the adjacent edges thereby placed in a closely-spaced or abutting relation. A liquefied thermoplastic material (preferably, polypropylene) is then applied to the exposed surface of the wound strip, and a roller is formed by helically winding the cover over the liquefied material and the wound strip with sufficient tensile force so that the fabric cover lays smoothly thereupon. Again, as with other endless roller manufacturing, a fly-away cutter may be first used to cut the product into longer lengths, and then such lengths may be cut to usable lengths. This process represented an advance over the previous method invented by the present inventor because the entire paint roller was formed in a single step which made the assembly line easier to manage as there was only a single strip of material and a single application of liquefied thermoplastic. The resulting roller, however, is somewhat inferior. More specifically, a defect present in all such rollers, manifests itself as a weak point, often sticking out from the ends of a cut roller, or making the ends of the cut roller appear "out of round." This results from the high tension memory of the strip which tends toward unwinding or toward "open" with high hoop strength. Moreover, to achieve the desirable hardened feel of the multi-layer rollers, the single strip rollers are generally made using a thicker plastic strip. The thicker the plastic strip used, (especially in relation to the diameter of the core) the more pronounced the memory effect appears on the roller.
Another process for manufacturing thermoplastic paint rollers was disclosed in a very recently issued patent application. Specifically, U.S. Pat. No. 5,862,591 discloses another method of forming a paint roller in a single step. In this process, strips of thermoplastic are not used, and instead, a fluidized polypropylene is applied directly to a mandrel, and a cover is placed thereupon. The application of fluidized polypropylene to a mandrel has concomitant complications in synchronization and in the problems inherent in working with consistency of application of a fluidized layer in forming a polypropylene core. Like this process, other proposals have been made for placing the pile fabric on a heated core, as for example in French Patent Publication 2,093,060, in which pile fabric is placed on a hot, freshly extruded core. It is, however, believed that no such system has gone into practical use, possibly because of the difficulties associated with controlling the shrinkage variation which inevitably occurs in the matching of what is essentially a through heated core blank or strip blank and a cold (i.e., room temperature, for example) pile fabric.